This invention relates to a plastic fastener which is provided on its leg portion with stepped fin-like engaging projections and which, therefore, can be inserted with slight force into a fitting hole bored in a given panel and brought into powerful attachment without any play to the panel irrespective of the thickness of the panel.
A fastener which has a multiplicity of stepped engaging projections provided on a leg portion thereof so as to be attached fast to a fitting hole of a panel by virtue of the engaging projections has already been known to the art. The leg portion of this fastener having a multiplicity of engaging projections extended outwardly has the appearance of a Christmas tree. Thus, this fastener is generally called a Christmas tree type fastener or simply a tree type fastener. This fastener attains fast attachment to the panel by having one of the engaging projections caught fast on the edge of the fitting hole. The leg portion, therefore, acts as a common truck for supporting the engaging projections fast in position. The leg portion does not come into direct contact with the fitting hole. The fastener is constructed so as to secure fast attachment to the fitting hole only by means of the flexible engaging projections.
If the leg portion of this fastener is inclined during its insertion into the fitting hole, it is suffered to advance into the fitting hole and come into engagement with the fitting hole in the inclined posture. This problem entails a serious effect particularly when the fastener holds on the head portion thereof some other part fast in position. In the worst case, the fastener set in an inclined posture cannot be aligned with other parts and, consequently, fails to play the role of a fastener.
Moreover, since this fastener relies solely on the engaging projections for fast attachment to the fitting hole, there is a possibility that the fastener will be attached eccentrically to the fitting hole or, after attachment, will change its position relative to the fitting hole and will consequently be unstably attached to the fitting hole. This unstable fastening entails a problem that the fastener produces some play in the fitting hole.
Further, since the conventional fastener has the engaging projections extended perpendicularly from the leg portion, the force with which the fastener is inserted into the fitting hole equals the force with which the fastener already attached to the fitting hole is pulled out of the fitting hole. For the fastener to be retained powerfully in its attached position, namely for the fastener to offer ample resistance to the external force tending to pull the fastener out of the fitting hole, therefore, the force used for inserting the fastener into the fitting hole is inevitably required to be equally strong. Thus, the conventional fastener suffers from notably poor workability.